Problem: 3 folders cost $3.63. Which equation would help determine the cost of 12 folders?
Solution: There are several equations that could help determine the cost, each with a slightly different approach. We know the cost of 3 folders. We want to know the cost of 12 folders. We can write the numbers of folders as a proportion: $\dfrac{3}{12}$ We know 3 folders costs $3.63. We can let $x$ represent the unknown cost of 12 folders. The proportion of these costs can be expressed as: $\dfrac{\$3.63}{x}$ The cost changes along with the number of folders purchased, and so the two proportions are equivalent. $\dfrac{3}{12} = \dfrac{\$3.63}{x}$